AC question about partial operation

I did use the search function so I appologize if I am repeating questions that have already been answered but most of the threads are very very in depth and I guess I have more of a general question about whether to spend any money....

I have a 98 XJ Limited (AW4) with 138k on it. I bought the Jeep in December so AC hasn't been an issue but I was driving for 2 hours yesterday and it was a tad warm so I clicked on the AC. Here's what I got......perfect cold air....for about 20 mins. The AC clutch engaged, I could appreciate a slight increased load on the engine as the compressor cycled on and off. After 20 mins.....I could no longer feel the compressor switching on and I lost all cooling from the vents. My question is....is this typical of low refrigerant, or more indictive of a larger problem? I only ask because I don't want to spend money on refrigerant or an AC shop only to find out the compressor is toast or the receiver/dryer is garbage or something like that. I live in Oregon so AC isn't that big a deal but it would be nice that if it worked consistantly. For $60-100 I can get the refrigerant refilled but I don't want to waste my time or money if that won't help...

Any suggestions? Thank you for your time.

It sounds symptomic of a failed low pressure switch, which is very common. What is happening is that your evaporator coils inside the cab are icing up and blocking air flow. That's why you feel cool at first, then the temp turns to luke warm. Once the ice melts, you repeat the cycle.

Next time this happens and you've let your XJ sit a while, check under your rig and you'll probably see a large puddle of water....that's all the melted ice.

Just replace the low pressure switch. It's located on top of the accumulator...black tank like looking thing near the fire wall. Just follow the refrigerant lines from your compressor. There's a schraeder valve on the accumulator, so you won't loose any refrigerant when you replace the faulty switch.

Thanks Ivan for the advice. Do I have to open the Shraeder valve prior to installing the new switch to prevent refrigerant from escaping? I'm fairly mechanically inclined but I don't have a lot of experience with AC systems. The switch itself seems fairly cheap so I think I'll pick one up and see if that fixes the problem. When the system was working it was blowing ice cold air so hopefully I still have good pressure.

No need to mess with the Shraeder valve. It's on the accumulator so that the low pressure switch can be changed out in case of failure, with out your AC system losing charge. Just remove the old low pressure switch, and replace it with a new one...

i had this exact same problem. Would work for 20 mins then would just pack up! My problem turned out to be a quick and easy fix. The gap that exists between the clutch plate and the comressor itself is seperated by tiny shims. The comressor would work initally for the first 20 mins, but as the change in temp of the metal components between clutch plate and comp changed this in turn caused this air gap to increase pass a point that the comp was no longer in a position to suck the clutch in to engage the ac. Clutch plate was removed, then one of those tiny shims, clutch plate put back on and bingo! That was last year and been working fine since. Bear in mind that my air gap was within spec but for some reason the magnetic pull of my comp was not great enough to pull the clutch in once things got up to operating temp so maybe my comp is not operating as it should but with that shim gone, its 100 percent ICE COLD air for however long i want! Also your problem may well be the low pressure switch as mentioned above, however a puddle of water under your car after being sat at idle a while with the ac on, i would suggest is normal and not a sign in itself that you need to get a new switch but i maybe wrong.

Good point about the AC clutch, as that was the next item that went out on my AC system, about 8 months after I replace the low pressure switch. I wound up replacing the compressor itself at that point, because a clutch replacement by the dealer was nearly half the cost of a whole new compressor.

Correct also on the water under the vehicle as being normal, albeit it's usually not that large of puddle. I should have clarified that a LARGE puddle of water is a good indicator.

This is great advice guys...thank you very much. I ordered a low pressure switch yesterday and for $14 I'll take a shot that that will take care of the problem. I should be able to replace it this weekend and update this thread as to whether that took care of the problem before I start focusing on the compressor clutch. Is the clutch difficult to remove? Do you have to evacuate the system before you start disassembly?

Im sure someone will correct me if im wrong as i didnt do the procedure, but i watched an a/c guy do it for me. Basically you dont need to evacuate. Remove the serp belt, then just undo the central nut that sits in the middle of the clutch. remove the clutch plate from its shaft, then CAREFULLY remove one of the shims from that shaft (they are very easy to loose). I believe there are a number of these tiny shims maybe 2, 3 or 4 possibly more. Just remove one at a time unless you know its way off spec. I cant remember of the top of my head what this gap should be (but its like credit card thickness which mine was already). Then with that TINY shim removed, put the clutch plate back on and do the bolt back up. It took this a/c guy no more than 5 minutes max to complete and its worked 100 percent ever since. On mine it would cycle correctly for the first 20 minutes and be nice and cold during that time but then the clutch simply wouldnt engage and the air would blow out luke warm.
Im almost certain also, that another symptom was the a/c fan failed to engage once the compressor stopped sucking in that clutch. Note, It wasnt the clutch that needed replacing, nor was it the compressor. I just had one of the shims removed and its worked ice cold for the whole of last summer and so far good this year too. The a/c that i get out of my jeep is also way, way colder than any other car i have ever owned!!!
good luck and PLEASE do update the result
many thanks

dunbad, it's cold because it's American! US cars definately have the best AC in the world.

Ivan, I'm trying to learn from your experience. I have been a student of AC issues for the last 8 years (due to my recently terminated employment). How do you figure that a low pressure switch could cause icing? It seems possible to me that the high pressure switch could do that, but low pressure is the result (IMHO) of low refridgerant level, which causes not so cold temperatures on the evaporator.

98NWCherokee said:

This is great advice guys...thank you very much. I ordered a low pressure switch yesterday and for $14 I'll take a shot that that will take care of the problem. I should be able to replace it this weekend and update this thread as to whether that took care of the problem before I start focusing on the compressor clutch. Is the clutch difficult to remove? Do you have to evacuate the system before you start disassembly?

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Just run your Jeep until it stops getting cold. Then look at your clutch center. You can tell if the clutch is engaging enough by watching it. Look at it when you first start it up and it IS making cold air. Clutch clicks in and spins center shaft. Clicks again and stops spinning center. Etc. Easy. Now, if it stops getting cold and clicks in and out without spinning the center, it is the clutch (adjustment, probably). Don't go throwing parts at your Heep without the proper diagnostics. It's a good idea to find out what helped other people with problems and get ideas about what to check out, but don't jump to conclusions that their fix will fix yours.

winterbeater said:

dunbad, it's cold because it's American! US cars definately have the best AC in the world.

Ivan, I'm trying to learn from your experience. I have been a student of AC issues for the last 8 years (due to my recently terminated employment). How do you figure that a low pressure switch could cause icing? It seems possible to me that the high pressure switch could do that, but low pressure is the result (IMHO) of low refridgerant level, which causes not so cold temperatures on the evaporator.

Click to expand...

The low pressure switch issue was diagnosed by the dealer while my XJ was still under warranty. In talking with the mechanic at the time, he had told me that there seemed to have been a rash of those issues occurring.

Here is a post that I cut 'n pasted to my Tech folder which should point you in the right direction:

"AIR Cond TSB:
There are two Jeep (Oops, sorry. "Daimler-Chrysler" Technical Service Bulletins (TSBs) out on late model Cherokees that you might want to check into. One deals with replacing the low pressure cycling switch (TSB #24-13-99) (97-99 XJs and TJs) to prevent evaporator freeze-up and subsequent refrigerant leaks. The other (TSB #24-13-97) (97-98 XJs and TJs) points out a common leak at the AC hose manifold on the compressor. AC leaks in 97-99 XJs seem to be pretty common. I'm suprised that Jeep/DC hasn't stepped forward and admitted the problem(s)."

And another one I saved.....

"AC Check procedures:
Jeepers , some things to check.
1. Does the compressor come on at all?
2. If it comes on does it cylce on and off? 2 things cause the compressor to cycle.1.the low pressure switch on the accumulator by the firewall. and 2. the thermistor on the evaporator.
3. If the compressor did not run unless you jumped out the switch on the accumulator, then the refrigerant pressure was to low(low refrigerant level) or faulty switch.
4. If the compressor runs when you jump out the switch, set the controls to max a/c and the fan on high. Stick a thermometer in the middle vent to read the temp. it should be 34- 40 degreesF. Any lower and the evaporator will freeze up. This will block airflow and cause warm or hot air to come out the vents, although with less force.A defective thermistor will cause this condition.The thermistor senses evaporator temp and cycles the compressor off/on.
5.If low refrigerant is the culprit , charge the system with R 134A one can at first , checking the vent temp while doing so.Add refrigerant at the accumulator. If more than one can is needed there is a leak in the system.Look for signs of oil around any a/c hoses or fittings, as well as around the compressor.
6. If you add refigerant add one can of refr. oil (it cimes in a smaller can). Add it the same way as the refrigerant.
7.One tip, when adding refrigerant , wrap the can in a warm towel or partially submerged in warm water to speed up the process.

Sorry about being long winded, but check everything you can , as compressors are not cheap and when they are replaced you must change the accumulator also. Otherwise the compressor warranty will be invalid. The accumulator absorbs any moisture in the system to protect the compressor."

You are right... someone's issues could be completely different than what one experiences with their own. That's what is awesome about forums such is this, because you can draw from other's experiences to help solve your own...

damn right winterbeater! I want a/c to be ice cold! forget this ambient talk you get from euro carmakers! IF it gets too cold, i save fuel and turn it off for 5 mins! The same for the winter, i want burn your face heat when theres inches of snow on the ground! Also 98nwcherokee, winterbeater has given some sound advice, from your issues there could well be a hundred different causes, thats what i learnt about jeeps anyway. Each jeep has an invisible gremlin inside right from the day it leaves the factory. Symptoms, causes, solutions often mean nothing to this gremlin! so alot of people will say to start as easy, simple and cheap as you can and work up. Very often the fix is not as bad or as costly or complicated as people assume. Ok, so sometimes its worse! But for info my jeeps clutch failed to even make that click sound once that 20 min mark had passed. It just sat there, didnt rotate or get sucked in or pushed outwards. Just silent and still until i shut it off and let everything fully cool down before firing her up again. If i restarted her during the cooling down process she would behave for a few minutes before the gremlin started his involvement.

My 97 did the same thing. Man, talk about a waterfall after I parked it on a 95* humid day after sitting in traffic on the NJ Turnpike for an hour on the 4th of July. You will notice that although it will "sound" like it's ok, very little air is actually coming out of the vents. That's because of the ice blocking the evaporator. I used to switch it to a non-ac position and it would melt VERY quickly.

It takes about 2 minutes to swap the switch out. My wife thinks it took two hours (and alot of beer).

Ivan, thanks for the extra information. By the way, when I was working warranty on HVAC systems, we would get dozens of thermisters every month which were changed our due to icing. In over a year and a half and probably 300 thermisters tested, only one was actually bad.

To prevent freeze up, keep windows closed and don't just run fan on low. Using recirc mode (max AC) also helps because you are recirculating air that has already been dehumidified. The probelm is the greatest on high humidity days.

winterbeater said:

..... The probelm is the greatest on high humidity days.

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Funny you should mention that... I live in an area where the relative humidity averages 70% - 80% year around, with about 40 inches of rain annually. Thank gawd the record high temp has never exceeded 81 degrees. I'm glad the average high temp is about 53 degrees, or I'd be all sorts of miserable with this much humidity....

Just to update this thread.....I'm still waiting for the low pressure switch. I guess no one stocks these so I've been having a hard time tracking one down. I should have a new one in a day or so and I'll put it in and report back. It was hot this weekend so I had lots of opportunities to fiddle with the AC. I pretty much got the same results.....operation about half the time but I did notice what I would call a large puddle of water under the Jeep after the AC had been working. This might be the ice melting that was mentioned earlier if in fact my low pressure switch isn't working. It definitely seemed like more water than I'm used to seeing from AC systems.

I thought I would revive this thread since I was finally able to install the low pressure switch last night after waiting 3+ weeks to get one. The switch does not appear to be the problem, although it sure was easy to install. After installation I started the Jeep and kicked on the AC. The electric fan kicked on, but no compressor. I killed the engine and check the connection on the switch(it was good). I re-started the engine and BOOM the clutch engages.....for about 5 mins. I watched it closely and after 5 mins of cycling on and off perfectly the compressor started to kick on again. It did about a 1/8th turn and then stopped and did not kick on again. I checked the lines and they were ice cold. During the 5 mins of operation it worked perfectly and blew cold. I suppose my next step is to try removing a shim on the compressor clutch. I removed the shroud last night but couldn't figure out how to remove the clutch pack. Is there a trick to this? Do you have to insert a screwdriver or something to get leverage for a wrench? Any help would be much appreciated.

The FSM shows a special tool to hold the pulley stationairy while removing the nut, then using a puller. They take the compressor mounting bolts off first to turn the compressor into a better position for this. Maybe a strap wrench on the pulley would work. Hopefully someone who has actually done it will help with the advice here. The gap should be .016"-.031".

I actually fixed the gap problem on mine (Brand new clutch and compressor was over gapped) with a screw driver by just bending the tabs between the inner and outer part of clutch. That was 4 years ago.

ok, so im using this thread instead of starting a new one...

heres my problem, its a 105 degrees out here in CA about 15% humidity... is there a reason why im not getting ice cold air from my 2000 xj with the 4.0 automatic? motor has about 114K miles and the a/c was serviced but giving the service guy crap before it finally got fixed... this is the first really hot week we've had, im just curious if its the a/c or its just the external heat, cuz my a/c is running full time in my apartment and wont get below 80 degrees lol, fans on high the whole deal =/